Google’s advertising service for website publishers, launched in 2003, was called AdSense.
AdSense allows publishers to display targeted advertisements on their websites and earn revenue when visitors interact with those ads. Google introduced the service after acquiring Applied Semantics, whose technology helped match advertisements with webpage content.
The program became a major part of Google’s advertising ecosystem because it extended Google’s advertising business beyond its own search-results pages. Website owners could place code on their pages while Google handled ad selection and much of the commercial process.
AdSense is often confused with AdWords, now called Google Ads. AdWords was aimed primarily at advertisers buying campaigns, whereas AdSense was designed for publishers displaying those campaigns.